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G. P. HULST AND M. w. Kmsll.

PROCESS 0F TREAT|NG LEAD BULLION. APPLICATION FILED FEB. 1s, 1920.

1,386,503, y Pantemug. 2,1921.

2 S HEET l. Z

G. P. HULST AND M. w. KREJEI.

PROCESS 0F TREATING LEAD BULLION.

APPLICATION FELED FEB. I6, 1920.

Patented Aug. 2, 1921.

2 SHEETS-SHEET 2 UNITED STATES PATENT OFFICE.

GEORGE 1. HULST, OF HAMMOND, INDIANA, AND MILO W. KRE-TCI, OF CHICAGO, ILLINOIS.

PROCESS 0F TREATI'NG LEAD BULLION,

Specification of Letters Patent.

Patented Aug. 2, 1921.

Application led February 16, 1920. Serial No. 359,069.

To all 'whom it my concern;

Be it known thatwe, GEORGE P. HULST, and Mino W. KREJI, citizens of the United States, residing, respectively, at Hammond, in the county of Lake, State of Indiana, and at Chicago, in the county of Cook, "State of Illinois, have invented certain new and useful Improvements `in Processes of Treating Lead Bullion, of which the 'following is a full, clear, and exact description, reference being had to the accompanying drawings, forming a part hereof.

The present invention is directed to the refining or purification of lead bullion, particularly in connection with the well known Parkes process of desilverization. It may be considered as an improvement on the process forming the subject-matter of U. S. Patent No. 1,285,714 bearing vdate Nov. 26, 1918, issued to George P. Hulst, process of treating` lead bullion, the object herein sought being, among other things, to cut out the softening and preheating furnaces made indispensable in the patented process; to reduce the amount of material treated at the retort and cupels, through the higher concentration of silver in the Zinc skim from the desilverizing kettles; to reduce the amount of Zinc involved in the deslverizing operation; to secure a richer copper dross .from the treatment or drossing kettle for the residue furnace; to eliminate practically, the formation of copper litharge in the cupel furnace to eliminate the formation of copper skim in the desilverizing kettle; and finally, to simplify the process as a whole whereby a material saving Vin the cost of production results. Generically, the invention contemplates the incorporation into, and diffusion through, abath of molten bullion maintained at proper temperature, of a suitable reagent (or reagents) having sufficient affinity for the various impuritiesv (copper, arsenic, tellurium, selenium, antimony, bismuth) contained therein, to segregate the same from the lead and bring them to the surface of the bath in the form of a dross that may be skimmed ofi', leaving the lead in a pure conderived from refiner skim, molding skim, Pattinson skim or from any other suitable source) in conjunction with sulfur or any suitable sulfur bearing compound having a drossing action on the copper content of the lead. The character of thedross formed by the addition of the respective reagents to the lead bath lwill obviously depend on the nature and relative quantities of the impurities present in the lead; and while impurities such as arsenic, tellurium, selenium, and antimony may be drossed out by means of the aforesaid alkali hydrates or carbo-hates, and arsenic and antimony may be dresse-d out by means of lead oXid; yet, unless we add sulfur or some sulfur bearing compound to the bath, the copper will remain behind, except such portions as ordinarily dross out by liquation as practised in the art, this drossing being materially assisted by the sulfur which is usually present in small quantities in base bullion. bince copper is perhaps the most objectionable element to contend with in the desilverizing operation, it follows that under our improvement resort `must be had to sulfur or sodium sulfid or sulfate or their equivalents) to rid the lead of its copper before desilverization is attempted, the addition of the ,sulfur` reagent being necessary even though use be made of some of the other compounds (the hydrates or carbonates of the alkali metals, or the oXid of lead) for the elimination of impurities other than copper. Sulfur has the capacity of dressing copper, arsenic, selenium, and tellurium, the sulfid or sulfate of sodium drossing in addition the antimony. Precisely what reactions between the drossing reagents and the impurities in the lead take place, and what the exact compositions of the various drosses are We are not prepared to say; neither is it important that we know. The fact is that when these reagents or any of them are used and applied as hereinafter described they dross the impurities out of the bullion. When sulfur alone or uncombined is added to the hot lead the dross formed thereby is probably a mixed arsenid, tel-lurid, selenid and sulfd of copper; when sodium sulfid or sulfate is added to the bath the dross is probably a mixture of arsenid, tellurid, selenid, and sulfid of copper, and arsenate, tellurate, selenate, and antimonate of sodium, it being remembered that sulfur uncombined will not dross the antimony, whereas a sulfid or sulfate of sodium will; when a hydrate or carbonate of an alkali (such as soda or potash) is added to the bath the dross'is probably a mixture of al'senate, tellurate, selenate, andi ployed in conjunction with sulfur because while sulfur will not dross the antimony, the

lead oxid will, the result being substantiallyv that'obtained with .theuse of' an alkali metal suld or sulfate which, aspreviously pointed out dresses not only the copper, arsenic, tellurium, and selenium but the antimony (and arsenic) as well. Of course, wit-h all these dresses there will always be mixed some lead probably in the form of oxid by reason oit the incidental oxidation which necessarily results during the incorporation et the reagents into the het bathv of metal. Nothing has been said about bismuth; .butsince rthis does not materially afliect the desilveriZi-ng` operation, and since it is doubtful that any material dressing of this metal results from the addition of any reagent here used, we may dismiss this element from further consideration, allowing it to be disposed of in the final refining operation by any suitable method known in the art. lNe' do not wish to be understood that the vformation ot dross due to .the addition tothe lead bath ot any of the reagents above mentioned, it being wel] known that dross carrying various impurities is formed in the liquation of lead bullion in the Parkes process, and that certain inipurities in the form of a skim rise to the surface of the lead bath in the oxidizing` step of the softenino oper/ation. The same is true of the process described in the Hulst patentatoresaid. rEhe novelty of our invention does not reside in the formation oi' dross, but 1r. the process by which the impurities in the form of dross are ractically entirely elimil nated from the lea leaving the latter in the best possible shape for desilverization. By the process described in theV Hulst patent aforesaid, it was considered quite an accomplishment to bring the copper content in the liquating kettle ldown to .05%. As an example of what can be accomplished by our improvement may be cited the tact that in one case where an assay of the bullion before treatment showed .164% otcopper, an assay after treatment showed that the copper had been reduced to .0008 (eight ten-thousandths of one per cent), the arsenic being.

Ydispensing with the softening turnace and 'the preheating furnace, and thus reducing the cost per ton of bullion treated, the value o1 our improvement will be appreciated. In

practice, the reagents are added to the charge oi bullion in proportions conforming 'substantially to their combining weights. For example, if using sulfur, about two hundred (200) pounds oit .the sulfur preferably in powdered form are added to a rbath of ninety-tive to one hundred tons of molten lead, this being suiiicient to dross the copper out of the bullion (p'robablyinfthe torna` of a copper sulid). The weight of sulfur added to thev bullionv is approximately one-v tenthot1 'Oneper cent.. of the' weight of the" bullion. On the other hand, where sodium suld Na) is used, there, considerably more must be added Yto dross the copper on account of the lower quantity o t. sulfur pres'- ent in the suld, it being remembered that the sodium elementpprobably combines with the arsenic., tellurium, seleniuml and antimony to form the arsenates, tellurates, selenates and antinonates of sodium. By assaying the base bullion before treatment, the expert metallurgist can determine the approximate amountof reagent or reagents to be added. To insurethe results here out'- lined, the reagents must be thoroughly incorporated into and diffused througn the molten charge of bullion, andfin such manner as to impregnato the entire mass of lead. The matter of temperature, and the pressure involved in the methodot diffusing the reagent through the mass (lead bath) are controlling, because on these'depends the success of our process g' and while notwishingto restrict ourselves to -any one'apparatus for carrying on the process, that here shown has been found eminently Vsatisfactory in practice. The same comprises 'a stirring machine which may be deposited over any drossing kettle in whichv the lead is liquated, the metal being so stirred during the feeding ot the reagents thereto, as to bring about the necessary diiiusionfot the reagents through the bath, andthe thorough impregnation ot the bath thereby, during which time the tem-g of the kettle showing the horizontal rotary movement imparted to the metal when stirred; and Fig. 5 is a middle vertical section through the kettle showing diagrammatically the vertical radial circulation of the metal when stirred.

Referring to the drawings, 1 represents a conventional desilverizing kettle, 2 the brick work lon which the same is supported, and

F the tire place within the brick work as well understood in the art. In the present embodiment of our invention the reagents added to the molten metal or bullion B for the purpose of drossing the impurities, are incorporated into the lead and caused to be diffused therethrough by means of a stirring apparatus deposited overl the kettle,

this apparatus comprising a frame or platw form J built up of I-beams or equivalent structural members suitably tied and braced, one end of the platform supporting a preferably electric motor 3, the shaft t whereof is supported at its outer end by a post or bearing 5 approximately at the center of the platform, the shaft terminating in a bevel pinion 6 meshing with a bevel gear wheel 7 at the upper end of a vertical stirrer shaft 8 carried by the platform, the shaft being provided at its lower end with suitable radiating stirrer blades or arms 9. The gears 6 and 7 are preferably protected by a casing 10, a suitable cylindrical casing 11 secured to the platform P likewise protecting the stirrer shaft and its blades. The casing 11 is open atthe bottom, and near the top the same is provided with peripheral openings O for the free circulation of the molten metal.

ln the practical operation of the process, the bullion B in the dressing kettle 1 is first heated to approximately 700 degrees Fahrenheit or somewhat above the melting point of lead, and when this point has been reached the frame or platform P (which vtravels on a track overhead) is deposited over thel kettle as shown, the motor 3 is started and rotation (counter-clockwise in the present example) is imparted to the stirrer shaft 8 and its blades 9. The rotation of the stirrer mechanism imparts to the molten mass of metal a horizontal vertical movement or whirl, the core c of the vortex being concentric with the axis of rotation of the stirrer shaft 8. During the stirring of the hot metal the dressing agent m (sulfur or its equivalent) is thrown on top of the bath from a shovel S (Fig. 3) in the hands of the operator, or otherwise, and as the sulfur strikes the surface of the bath it participates in the rotary circulation or motion imparted to the metal and at the same time is drawn through the openings O toward the core o of the vortex, being sucked down into the body of the mass of metal; and with the pressure of the superincumbent metal upon them the sulfur particles circulate radially in vertical planes from and toward the axis of the vortex, the entire mass of metal with the drossing reagent diffused through it rotating in a horizontal plane and at the same time circulating in vertical radial planes as fully indicated by the arrows in Figs. l and 5. The dressing agent reacting with the 'impurities inthe lead drosses the same, the dross Z appearing on the surface of the bath from which it is subsequently skimmed. rhe stirring at the temperature aforesaid (700 degrees Fahrenheit) is continued for a period of say fifteen minutes, the dross at the conclusion of this interval being entirely skimmed off. rllhe temperature of the bath is then lowered say to about 660 degrees Fahrenheit, this lowering of temperature or cooling being accomplished either by adding more bullion or cold lead, or by blowing atmospheric air, steam, gas or Water through the bath by means of a pipe in the hands of the operator, or in any other manner known to the art. This lowering of the temperature al-V lows any copper which remains behindv to rise to the surface as a dross (probably as copper sulid) which is skimmed oil in the usual way and added to the irst skimmings. After this more sulfur (or other dressing reagent) is added to the bath while the same is being stirred and the resulting dress again skimmed and added to the previous skimmings. After this the bath is still further cooled to apoint where the lead begins to freeze and any final dross appearing is skimmed oil?. During the skimming of the dresses the stirrer may or may not be stopped. From the standpoint of economy the better practice would be to stop the stirrer while skimming. After the final cooling and skimming, the bath is heated up to a point slightly above the melting point of zinc (any dross appearing being skimmed off) and zinc added and stirred into the charge in the usual way for purpose of desilverzation of the bullion. The dross removed by the several skimming operations is subsequently heated in a kettle so as to melt the lead, and subjected to pressure by any form of press lowered into the kettle, the lead in the pressing operation being squeezed out and treated over again, the dry dross being charged into the residue furnace the same as in the process of the Hulst pat-` ent aforesaid. ln fact, the refining operation under our improvement is similar to that practised under the Hulst patent, except that by our method of dressing we dispense with the softening and preheating furnaces of the patented process, and it may be said that we likewise dispense with the liquating kettle therein referred. to, the

dressing by our method being` carried on in the desilverizing kettle to the puried bullion in which the Zinc is directly added at the conclusion of the dressing operation.

yOf course,`by the substantially complete elimination of the copper from the bullion under our improved method there remains only a negligible quantity of copper in the kettle when the Zinc is added so that the copper skim therefrom returned to the residue furnace is reduced to the minimum. For the same reason little or no copper litharge'will make its appearance in the cupel furnace under our improved method of treatment.` There being practically no copper in the desilverizing kettle when the Zinc is added, it follows that a less amount of zinc need be used under our improvement than was the case with the patented vrocess so too the co a* er drosses charo'ed from the kettle to the residue furnace are necessarily richer than the drosses from the liquating kettle in the patented process. ln said process the refiner skim, molding skim and Pattinson skim were employed as oxidizing agents in the softening furnace. rllhesel skims are in the main an oXid of lead, and may still be employed under our improvement for dressing the antimony should any be present in the bullion, in which event this oXid of lead could be added to the bath in proper proportions in conjunction with the sulfur component which drosses the copper and other impurities, the combined dross being charged into the residue furnace. lf the Y bullion contains no antimony or only a negligible amount, these lead oXid skims may be turned directly into the residue fur-- nace the same as in the conventional Parkes process. Under our improvement the dross bullion from the residue furnace is returned into the dressing kettle (the same as it is returned in the fulst patent to the liquating kettle), the matte going to the Crusher, and the antimony slag to the blast furnace, the same as in the patented process.

The stirring apparatus here shown and described for incorporating the dressing reagent (or reagents) into the molten bath, and causing the diffusion thereof throughout the molecules of the molten metal, is only by way of example. The same result might be brought about by other means. For example, the reagent (sulfur, or its equivalent) in powdered form might be blown into the body of the molten metal below the surface thereof by means-of an inert gas such as carbon dioXid or nitrogen (so as not to burn the sulfur), in pretty much the saine way as a charge is blown in a con-V verter, this method being understood by those skilled in the art and requiring no illustration. To secure the desired incorporation and diffusion of the reagent the element of pressure is more or less controlling; F or example, in the case ofthe stirrer.

apparatus here shown, as the particles of" sulfur are drawn by the vortex into the body of the molten. mass the same are caused to circulate therethrough while sub]ected to the pressure of the superincumbent bodyA fused therethrough wouldy come within-the scope of our invention, the object sought in all cases being to effect the incorporation and diffusion in such a way as not to subject the reagent to oxidation' before it has had a chance to ieact withthe impurities to formV dross. )Vith .our present stirrer, it is true that as the sulfuris being fed-to the bath some of it (a very small fraction) takes re and is converted into gas (SO2), which escapes, but this quantity is quite negligible. ln the present example we show the sulfur as being thrown into the bath by a shovel in the hands ofthe operator, but any form of mechanical feed may be substituted. In fact we may provide the stirrer with a feed attachment for the sulfur (or other reagent) to designwhich would fall within the purview of the skilled mechanic.

lt was pointedout above that the temper.- ature at which the initial dressing in the kettle is practised `should be approximately VTOO degrees Fahrenheit. This of course is above the melting point of lead but considerably below the melting point of copper. The reason for this temperature is, that were the metal made any hotter there would be danger of a part of the copper remaining behind in the bath, the obj ect sought being to maintain the temperature comparatively low so as toy insure the complete segregation ofthe copper iny the form of dross (whose melting v point is higher than that of the lead). After the first dressing the temperature is progresl sively reduced until all the copper is eliminated as previously describedl Any reagents that operate' as chemical equivalents of those here mentioned are necessarily included within the scope of our invention. Again, the process need notV necessarily be restricted to the treatment-of base bullion as it leaves the blast furnace, but may be applied to bullion which has subsequently been softened A but vfrom which the copper has not been completely removed.

Having described our invention whatwe claim is: Y Y

l. In the treatment of lead bullion, the

process `which consists in subjecting a bath of molten lead to agitation, and simulta-iv neously feeding thereto without oxidation a suitable reagent operating to segregate therefrom the impurities in the form of dross.

i 2. ln the treatment, of lead bullion, the process which consists in subjecting to agitation aV bath of'molten lead maintained at a temperature below the melting point ofV copper, and simultaneously feeding thereto a suitable reagent operating to segregate therefrom the impurities inthe form of dross. 'f

ln the treatment of lead bullion, the processs which consists in subjecting to agitation a bath of'molten lead maintained at a temperature above its melting point and below the melting point of copper, and simultaneously subjecting said bath to the action of a reagent carrying sulfur operating to segregate therefrom the impurities in the form of dross.

et. ln the treatment of lead bullion, the process which consists in subjecting a bath of lead maintained at a temperature below the melting point of copper, to the action of sulfur reacting with the impurities in the lead below the surface of the bath whereby said impurities are dressed and caused to rise to the surface.

5. ln the treatment of lead bullion, the process which consists in melting a charge of lead and maintaining 'the temperature thereof below the melting point of copper, and diifusing through the mass a sulfur carrrying reagent whereby the impurities are dressed and caused to rise to the surface of the bath, then removing said dross.

6. ln the treatment of lead bullion, the process which consists in melting a charge of lead and maintaining the same at a temperature of substantially 700 degrees Fahrenheit, causing a diffusion through the mass, of j a sulfur carrying reagent for dressing out the impurities, removing-the dross, reducing the temperature of the bath to cause any copper remaining behind to rise to the surface as a dross, removing said dross, repeating the diffusion through the mass of a sulfur carrying reagent at such reduced temperature, removing the resulting dross, then again further reducing the temperature until thel freezing point of lead is approached, then nally heating the lead to bring the bath to proper temperature for desilverization and at the same time skimming od Vany dross floating on the surface of the bath.

7. ln the treatment of lead bullion, the process which consists in subjecting a bath of vmolten lead to vortical rotation about a vertical axis and simultaneously causing a radial circulation of the molecules to and from said axis, feeding to thesurface of said bath a dressing reagent whereby the same is drawn into the core of the' vortex and then caused to pass into the mass of the lead by the radial circulation of the moleculesl as aforesaid, thereby permeating the mass andreacting with the impurities to 'form a dross which rises to the surface of the bath around the core of the vortex, and finally removing the dross.

t3. ln the treatment of lead bullion, the process which consists in diffusing through a. charge of the molten metal a suitable reagent to dross thc copper content of the charge, maintaining the temperature of the bath below the point of fusion of the copper, then removing the dross.

9. ln the treat-ment of lead bullion, the )recess which consists in diffusing below the surface of a charge of the molten'metal a .sulfur carrying reagent reacting with the copper content of the charge to form a copper dross, maintaining the temperature of the bath above the melting point of leadV but below the melting point of copper, skimming the dross, then cooling the bath to clear the same of the balance of the copper in the forni of dross, and removing the sec-A ond layer of dross. Y

l0. in the treatment of lead bullion, the process which consists in forming a bath of molten lead, incorporating a dressing reagent into the mass by agitation of the mass, and finally skimming the resulting dross.

ll. ln the treatment of lead bullion, the process which consists in forming a bath of molten lead, causing a dressing reagent .to penetrate the mass below the surface ofthe bath, and skimming the resulting dross.

l2. ln the treatment of lead bullion, the process which consists in forming a bath of molten lead, causing a sulfur reagent to penet ate the mass below the surface of thebath, and finally removing the resulting dross.

ln the treatment of lead bullion, the process which consists in forming a bath of molten lead and maintaining the same at a temperature between the melting points of lead and copper, causing a dressing reagent to be diffused through the mass by pressure exerted against the molecules of the mass, whereby impregnation of the lead by the reagent results and the impurities thereof are expelled in the form of dross which rises to tne surface of the bath, then removing the dross.

l-l. ln the treatment of lead bullion, the process which consists in forming a bath of molten lead, agitating the mass, and simultaneously introducing thereinto at a point beneath the surface thereof a reagent operating to dross the impurities.

l5. ln the treatment of lead bullion, the process which consists in forming a bath of the molten metal, and causing a suitable reagent to di'use itself while subjected to the pressure of the mass, through Vthe mass, thereby segregating the impurities from the lead in the form of dross.

16. ln the treatment of lead bullion, the process which consists in forming a bath of the molten metal7 and introducing into the bath against the pressure exerted by .the molecules thereof a suitable sulfur reagent whereby the reagent thoroughlyT impreg-v nates the mass and combines With the impurities to form a dross, then removing the dross.

17. In the treatment of lead bullion7 the process which consists in forming a bath of the molten metal, then forcibly introducing between the molecules of the mass a suitable sul fur or equivalent reagent to combine with the impurities to form ya dross, then removing said dross.

18. In the treatmenty of lead bullion, the process which consists in subjecting a bath of the molten metal t0 the action of a suitable reagent caused :to permeate the mass of metal and react -With the impurities there of to form a dross which is removable from the surface 0f the bath.

YIn testimony whereof We .affix our signaturesI respectively at'Hammond, county of Lake, State .of Indiana, the 7th day of F ebruary 1920,V and at Cleveland, county of luyahoga, State of Ohio, the llthvday of February, 1920.

GEORGEY P. HULST.

MILO KREJI. 

